1. Field of the Invention
The present invention relates to a surface acoustic wave device for use in a resonator, a band-pass filter, and other electronic components, and more specifically relates to a surface acoustic wave device including a piezoelectric substrate in which an epitaxial LiNbO3 film is laminated on a sapphire substrate.
2. Description of the Related Art
In recent years, an increase in frequency has been required also in surface acoustic wave devices with an increase in frequency in communication apparatuses and the like. Moreover, in a surface acoustic wave filter and the like, an increase in band width has also been strongly required.
In order to achieve an increase in frequency and an increase in band width, it has been required that the acoustic velocity and the electromechanical coupling coefficient k2 of surface acoustic waves are high.
In order to satisfy the above-described requirements, Japanese Unexamined Patent Application Publication No. 10-322158 discloses a surface acoustic wave device 1001 illustrated in FIG. 32.
The surface acoustic wave device 1001 includes a piezoelectric substrate 1004 in which a LiNbO3 film 1003 is laminated on a sapphire substrate 1002. On the piezoelectric substrate 1004, input electrodes 1005 and output electrodes 1006 are provided. The projecting direction of the c axis on the sapphire substrate 1002 and the c axis direction of the LiNbO3 film 1003 are parallel to each other. Therefore, it is disclosed that the acoustic velocity and the electromechanical coupling coefficient k2 of surface acoustic waves can be increased by controlling the propagation direction of the surface acoustic waves.
In contrast, International Publication No. WO98/56109 discloses a surface acoustic wave device employing a piezoelectric substrate in which a LiNbO3 film is laminated on a sapphire substrate or a piezoelectric substrate in which a LiNbO3 film is laminated on a sapphire substrate.
According to the surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 10-322158 or International Publication No. WO98/56109, an increase in the velocity or an electromechanical coupling coefficient of surface acoustic waves has been achieved by the use of the piezoelectric substrate in which the LiNbO3 film or the LiNbO3 film is laminated on the sapphire substrate, i.e., R-plane sapphire substrate. However, in recent years, a further increase in frequency or a further increase in band width has been required, and thus an increase in the acoustic velocity and the electromechanical coupling coefficient k2 of surface acoustic waves has more strongly demanded.
Moreover, in order to achieve a reduction in the size of surface acoustic wave devices, an increase in a reflection coefficient has also been strongly demanded.